FR2720386A1 - Bridged clays prepn. - Google Patents

Abstract

Process for prepn. of bridged clay from natural or synthetic clay comprises: (A) contacting a clay having exchangeable cations with a soln. of polycations to form a reaction mixt. contg. 1-200 g/l of the clay; (B) maintaining the temp. of the reaction mixt. at 15-100 deg C and allowing exchange to take place between the polycations and the exchangeable cations in the clay for 1 min. to 3 h.; and (C) separating the resulting prod. by filtration and washing it, the time for the sepn. being 20 sec. to 60 mins. per litre of the soln. contg. the suspended prod. to be separated. Pref. polycations are Keggin ions of formula (A113O4(OH)24(H2O)12)<7+>, or polycations contg. at least one element chosen from Zr, Ti, Mo and V. Stage (A) may be carried out either by adding a soln. of the polycations to an aq. suspension of the clay, or by suspending the clay in a soln. of the polycations. Pref. the ratio R between the amt. of polycations multiplied by the charge on the polycation and the amt. of exchangeable cations present in the clay multiplied by their charge is between 0.5 and 10. The process may also comprise a fourth stage (D) in which the treated clay is first dried by heating in air at 30-150 deg. C for 2-48 h and then calcined at 300-800 deg C for 1-10 h. The treatment process may be repeated successively 2-10 times.

Description

The present invention relates to an improved process for carrying out the clay bridging operation. Said process applies to natural or synthetic clays.

Clays have the property of having expandable network structures, which allows them to absorb water. The structure of clays can be described, in a simplified manner, as a triple-layer sheet structure with a thickness of about I nm (1 nm = 10-9 m), constituting two layers of SiO4 tetrahedra separated by a layer of MX6 octahedra, M being a trivalent or divalent cation, such as for example A13 + in the case of dioctahedral clays or Mg2 + in the case of trioctahedral clays, and X representing an oxygen atom, an OH hydroxyl group or an atom fluorine F.

The silicon atoms of the tetrahedra can be substituted at least partially by aluminum atoms, and the aluminum atoms (respectively magnesium) of the octahedra can be substituted at least partially by magnesium atoms (respectively iron and / or lithium). These substitutions induce a deficit of positive charges, which is compensated by exchangeable cations such as Na +, Ca2 + or Li +, located in the interfoliar space (that is to say the spacing between two sheets).

The value of clays as catalysts or catalyst supports is limited to liquid phase catalysis because the clays expand when they are dissolved and undergo desiccation from the boiling point of the solvent. This results in a loss of their expanded character and, by the same token, a sharp reduction in the accessible surface, which makes them less advantageous in catalysis.

It is therefore necessary to maintain the expansion of the clays according to techniques which allow their use as catalysts or catalyst suppons, in particular in the field of refining and petrochemicals where one often operates at high reaction temperatures. .

One technique for maintaining the expansion of clays is bridging, consisting of introducing between the clay layers a mineral species which, after ion exchange and calcination, creates pillars. The clays thus obtained are generally referred to as bridged clays or even pillar clays.

The expansion of natural and synthetic clays is known. In order to carry out the bridging of clays, a technique well known to those skilled in the art consists in carrying out the bridging by oligomers of a hydroxide of a metal, or of cations leading to oligomers, such as for example aluminum. , zirconium or chromium. Thus, the bridging of clays is generally carried out by polycations [A11304 (OH) 24 (H20) 1217+ also called A113 cations or Keggin ions, or else polycations which may contain zirconium (for example in the form [Zr4 (0H) g (H2O) 16] 8+), titanium, molybdenum or vanadium, or even mixed polycations (for example in the form of [ZrOC12 Al8 (OH) 20i4 +).

The methods described (see in particular the publication by Yamanaka, S. and
Brindley GW "High surface area solids by reaction of montmorillonite with zirconyl chloride" Clays and clay mineraIs, p.ll9-124, (27), l9? 9, as well as the French patent application FR-A-2,512,043 and the PCT patent application WO88 / 06.488) generally implement the following successive steps - Mixing the solution containing the source of polycations with the
aqueous suspension of clay.

- Keeping in contact for a given time to carry out the exchange of
cations.

- Separation, by filtration or centrifugation, then washing or dialysis of
the exchanged clay.

- Calcination allowing the formation of the pillars.

Microporous materials with bridged lamellar structures can present an interest and interesting properties in catalysis, and in particular in the fields of refining and petrochemistry, and this in particular when the following conditions are met - the size of their porosity corresponds to that reagents and products of
reaction and induces high contact surfaces, - the thermal and hydrothermal stability of the bridged clays obtained is
such that the interfoliar spacing is maintained during the reactions
envisaged, - the method of preparing the bridged clays requires
of short exchanges, volumes of solutions containing the polycations
weak methods of filtration, washing and recovery of
products that are easy to process.

However, if the processes described in the prior art make it possible to obtain bridged clays whose interfoliar spacing and the contact surface are suitable for reactions in the field of refining and petrochemistry, said processes do not lead easily and fast to bridged products, or even for some to thermally and hydrothermally stable products at temperatures above 550 "C.

On the other hand, the processes for preparing bridged clays, described in the previous year, require i) very large volumes of polycation solution compared to the
mass of clay to be treated, ii) contact times between the solution of polycations and the clay very
lengthy, iii) methods of washing and recovering the final product which are
long and difficult to use on large quantities.

The object of the present invention lies in a process for preparing bridged clays from natural or synthetic clays.

The method according to the invention comprises at least one treatment of natural or synthetic clay comprising a first step of bringing a solution of polycations into contact with the clay to be bridged comprising exchangeable cations, thus forming the reaction mixture; then a second step in which the exchange between the polycations and said exchangeable cations is allowed to take place; and finally a third step in which the product obtained is separated by filtration and in which it is washed; said treatment being characterized in that - the mass of clay to be bridged per total volume of solution is between 1
and 200 g / l, preferably between 2 and 150 g / l and even more
preferred between 10 and 100 g / l, - the second exchange step is carried out at a temperature between 15 and
100 "C, preferably between 20 and 45" C and more preferably at
ambient temperature ; said second step has a duration of between
Minute and 3 hours and preferably between 2 minutes and 1 hour, - the separation time of the third step is between 20 seconds
and 60 minutes and preferably between 30 seconds and 40 minutes per
liter of solution containing the product to be separated in suspension.

As regards said first step, it is generally carried out according to one of the following embodiments: the introduction of a solution of polycations in an aqueous suspension of the clay to be bridged comprising exchangeable cations (first embodiment of the first step), suspending the clay to be bridged comprising exchangeable cations in the polycation solution (second embodiment of the first step). It is possible to carry out the two embodiments of the first step simultaneously, for example by introducing part of the polycation solution into a solution obtained by suspending the clay to be bridged comprising exchangeable cations in the. another panie of the solution of polycations or by mixing a first solution obtained by introducing a solution of polycations in an aqueous suspension of a part of the clay to be bridged comprising exchangeable cations and a second solution obtained by suspending the aqueous solution in water. another layer of bridging clay comprising exchangeable cations. Thus the first step is generally carried out according to the first embodiment and / or according to the second embodiment. For example and preferably, the bridging clay comprising exchangeable cations is introduced into an aqueous suspension thus forming an aqueous suspension of said clay, to which the polycation solution is added all at once and rapidly.

However, any embodiment making it possible to bring together a solution of the clay to be bridged comprising exchangeable cations and a solution of polycations is included in the context of the first step.

In all cases, said first step consists in bringing together fictitiously clay (powder) and a solution of total volume V, said volume comprising the volume of the polycation solution and optionally the volume of the aqueous solution which made it possible to suspending at least part of the clay; except for the error of the volume of the clay to be bridged, which is generally considered to be negligible in relation to the total volume, the total volume is therefore the volume of the reaction mixture.

The ratio R, defined as being the ratio between the quantity of polycations multiplied by the charge of the polycation and the quantity of exchangeable cations present in the clay to be bridged multiplied by their charge, is generally between 0.5 and 10, so preferred between 1.0 and 8.

The polycations usually used to carry out the bridging process according to the invention are [A11304 (OH) 24 (H2o) l2] 7+ polycations also called AI13 cations or Keggin ions, or else polycations containing at least one element chosen from the group. group formed by zirconium, titanium, molybdenum and vanadium, for example polycations in the form [Zr4 (OH) g (H2O) 1618+) or even mixed polycations (for example in the form of [ZrOCl2 Al8 ( OH) 20i4 +). However, any polycation capable of carrying out the bridging according to the invention is also considered in the context of the present invention.

As regards the third stage of the treatment, centrifugation is to be excluded insofar as the product obtained after this treatment has a low specific surface.

In a possible fourth final step, the clay is usually subjected to a heat treatment generally comprising two parts.

The first part of said treatment consists in drying the clay exchanged in air at a temperature between 30 and 150 ° C., preferably between 60 and 130 ° C. and even more preferably between 90 and 130 ° C. The duration of said first part of the treatment is between 2 and 48 hours. Then in the second part of the treatment, the product is subjected to calcination at a temperature between 300 and 800 "C and preferably between 400 and 800" C. This calcination lasts from 1 to 10 hours and preferably is equal to about 4 hours.

A variant of the process according to the invention is to implement, if necessary, several successive treatments such as that described above, each treatment optionally being followed by a final heat treatment step as described above, the number of these successive treatments being between 2 and 10, even more preferably between 2 and 5.

The process of the invention is suitable for all clays of natural or synthetic origin. The preferred clays are smectites, preferably montmorillonites, hectorite, beidellite rectorite, natural or synthetic, even more preferably, beidellites synthesized in an acidic and fluorinated medium.

The process according to the present invention makes it possible to obtain clays with pillars whose reticular distance dOol is at least equal to 1.0 nm, preferably at least equal to 1.4 nm and even more preferably between 1, 6 nm and 2.5 nm. The lattice distance, represented by doo I, represents the sum of the thickness of a sheet and the interfoliar spacing, the latter value being directly accessible by the conventional method of X-ray diffraction on oriented powder.

The clays synthesized by the process according to the invention exhibit good thermal stability and can therefore be used in the field of refining for applications such as hydrocracking, catalytic cracking, or the isomerization of paraffins and / or olefins.

The examples of the process according to the invention below illustrate the invention without, however, being limiting in nature.

EXAMPLE I
A sodium beidellite with the chemical formula Na0.5 (Si3.5A10.5) AI2Oî0 (OH, F) 2 for a half-cell is synthesized from a hydrogel whose composition is as follows: 1Si02 0.382 A1203 0.176 NaF 0 , 1 HF 48H20.

The ripening pH is between 4.5 and 5 and the crystallization time is 7 days at a temperature of 220 "C.

The crude synthetic product has a hydration rate of 9% by mass and the quantity of exchangeable Na + ions per mole of clay is 0.5. The B.E.T. is 59 m2 / g.

0.8 g of said beidellite are directly dissolved in 14.8 ml of a solution of Kegin [(All 304 (OH) 24 (H2O) 12] 7+ ions, the concentration of which is of the order of 9.10 ~ 3mol / 1 and the pH equal to 4. By way of example, this solution is prepared according to the procedure published by Urabe K. et al., Advanced
Materials 3 No. 11, (1991).

The mass of clay to be treated per total volume of solution is therefore 54 gn. The ratio R, defined as the ratio between the quantity of polycations engaged multiplied by the charge of the polycation and the quantity of sodium present in the beidellite, is 1.

After an exchange period of 7 minutes with stirring at room temperature and a filtration step of 1 minute, the product is washed with distilled water for 2 minutes, then dried at 90 ° C. overnight (approximately 15 hours) . The mass of beidellite after ion exchange and drying at 60 ° C. is 0.85 g. The reticular distance d00 1 is of the order of 1.92 nm and the specific surface area measured by the BET method is of the order of 265 m2 / g. After 5 hours of calcination at 550 ° C. in air, the bridged clay thus prepared exhibits a reticular distance d00 1 of the order of 1.83 nm and a BET specific surface area of the order of 230 m2 / g.

EXAMPLE 2 0.8 g of the sodium beidellite prepared in Example 1 are suspended in 30 ml of the solution of [A11304 (OH) 24 (H2o) 12] 7+ ions described in Example 1. The ratio R used is 2. The mass of clay to be treated per total volume of solution is equal to 26.7 g / l.

After an exchange period of 5 minutes with stirring at room temperature and a filtration step lasting approximately 30 seconds, the product is washed with distilled water and then dried at 60 ° C. overnight (approximately 15 hours The mass collected is 0.82 g, the lattice distance is of the order of 1.93 nm before calcination and 1.61 nm after calcination. The BET specific surface is of the order of 230 m2 / g .

EXAMPLE 3 0.8 g of the sodium beidellite prepared in Example 1 are suspended in 60 ml of the solution of [A11304 (OH) 24 (H20) 12] 7+ ions described in Examples 1 and 2 The R ratio used in this preparation is 4.2.

The mass of clay to be treated per total volume of solution is 13.3 g / l.

After an exchange period of 5 minutes with stirring at room temperature and filtration for 2 minutes, the bridged clay is washed with distilled water and dried at 600 ° C. overnight (approximately 15 hours). The mass collected is 0.86 g and the lattice distance is of the order of 1.89 nm and the BET specific surface is of the order of 190 m2 / g.

After 4 hours of calcination at 600 ° C. in air, the bridged clay prepared above exhibits a lattice distance d001 of the order of 1.75 nm and a BET specific surface area of approximately 165 m2 / g.

EXAMPLE 4 0.8 g of the sodium beidellite prepared in Example 1 are suspended in 19 ml of a decimolar solution of zirconyl oxychloride from the ZrOCl2, 8H20 salt according to the procedure described by Yamanaka S. et al, Clays and Clay Minerals, 27 (2) pp 119-124, (1979). The R ratio is 4.3.

The mass of clay to be treated per total volume of solution is 4.2 g / l.

After an exchange step with stirring of 15 minutes at room temperature and a filtration step lasting about 30 seconds,
The clay thus bridged is washed with distilled water and then dried at 80 ° C. overnight (approximately 15 hours). The procedure described above is repeated successively two more times.

The mass of product collected is 0.75 g, the lattice distance dOOl is of the order of 1.93 nm and the BET specific surface is of the order of 194 m2 / g.

EXAMPLE 5 0.8 g of the sodium beidellite prepared in Example 1 are suspended in 2.54 g of a REZAL 67 solution marketed by the company
REHEIS COMPANY and 12.7 ml of distilled water. The ratio R is equal to 4.2. The mass of clay to be treated per total volume of solution is 63 g / l.

After an exchange of 5 minutes at room temperature, the whole is filtered.

The filtration step lasts 20 minutes. The product is then washed with distilled water and dried at 90 ° C. overnight (approximately 15 hours). The mass of product is collected is 0.88 g, the lattice distance d001 is of the order of 1, 91 nm and the BET specific surface is of the order of 196 m2 / g.

After 5 hours of calcination at 500 ° C. in air, the bridged clay thus prepared exhibits a lattice distance dot 1 of the order of 1.73 nm.

EXAMPLE 6800 mg of natural rectorite supplied by the Source Clay Minerals Repository of the University of Missouri under the reference RAr-I are dispersed in 14.4 ml of solution containing the Keggin ions. The cation exchange capacity of rectorite is of the order of 54 milliequivalent / 100 g (Brown G.

and Weir A, H, 1963). The specific surface of said rectorite is 46 m2 / g.

The ratio R used is 2. The mass of clay to be treated per total volume of solution is 55.5 g / l.

After an exchange period of 8 minutes with stirring at room temperature, the product is filtered for approximately 30 seconds, washed with distilled water and dried at 60 ° C. overnight (approximately 15 hours). The mass collected after drying is 0.76 g. The lattice distance is of the order of 2.67 nm. After 4 hours of calcination at 500 ° C. in air, the bridged clay prepared above exhibits a lattice distance of the order of 2. 66 nm and its specific surface is of the order of 196 m2 / g.

EXAMPLE 7800 mg of Beidellite supplied by the Source Clay Minerals Repository of the University of Missouri under the reference SBCa-1 are dispersed in 16.3 ml of solution containing the Keggin ions. The specific surface of said beidellite is approximately 21 m2 / g. The approximation R is 2. The mass of clay to be treated per total volume of solution is 49.1 g / l.

After an exchange period of 8 minutes with stirring at room temperature, the product is washed with distilled water (after having been filtered) then dried at 60 ° C. overnight (approximately 15 hours). The mass collected is 0.79 g, the lattice distance is of the order of 1.84 nm and the specific surface
BET is approximately 182 m2 / g. After 4 hours of calcination at 500 OC in air,
The clay has a reticular distance of 1.71 nm and its specific surface
BET is approximately 145 m2 / g.

EXAMPLE 8800 mg of the fraction less than 2 mm of a Wyoming montmorillonite supplied by the American Colloid Company under the reference Volclay SPV-X, are dispersed in 30 ml of solution containing the Keggin ions. The BET specific surface of said montmorillonite is 30 m2 / g. The ratio R is here equal to 2. The mass of clay to be treated per total volume of solution is 26.7 g / l.

After 8 minutes of contact with stirring at room temperature, the product is filtered for approximately 30 seconds, washed with distilled water and then dried at 600 ° C. overnight (approximately 15 hours).

The mass collected is 0.82 g. The reticular distance obtained is 1.84 nm. After 4 hours of calcination at 5000 ° C. in air, the lattice distance is 1.7 nm and the specific surface is approximately 221 m2 / g.

Claims (6)

1 - Process for preparing bridged clay from natural or synthetic clay, comprising at least one treatment comprising a first step of bringing a solution of polycations into contact with the clay to be bridged comprising exchangeable cations, forming thus the reaction mixture; then a second step in which the exchange between the polycations and the exchangeable cations of the clay is allowed to take place; and finally a third step in which the product obtained is separated by filtration and in which it is washed; said treatment being characterized in that - the mass of clay to be bridged per total volume of solution is between 1 and 200 g / l, - the second exchange step is carried out at a temperature between 15 and 100 "C; said second step has a duration of between 1 minute and 3 hours, - the separation time of the third step is between 20 seconds and 60 minutes per liter of solution containing in suspension the product to be separated r. 2 - Method according to claim 1 such that said first step is carried out according to the first embodiment, which consists in introducing a solution of polycations in an aqueous suspension of the clay to be bridged comprising exchangeable cations, and / or according to the second embodiment, which consists in suspending bridging clay comprising exchangeable cations in the polycation solution. 3 - Method according to one of claims 1 or 2 such that the ratio R, defined as being the ratio between the quantity of polycations multiplied by the charge of the polycation and the quantity of exchangeable cations present in the clay to be bridged multiplied by their load, is between 0.5 and 10. 4 - Method according to one of claims 1 to 3 such that the polycations used are polycations [A11304 (OH) 24 (H20) 1217+ or Keggin ions, or else polycations containing at least one element chosen from the group formed by zirconium, titanium, molybdenum and vanadium. 5 - Method according to one of claims 1 to 4 such that, in a fourth final step, the clay is subjected to a heat treatment comprising two parts, the first part of the treatment consisting in drying the clay exchanged in air at a temperature between 30 and 150 OC. and for a period of between 2 and 48 hours, and the second part of the treatment being such that the product is subjected to calcination at a temperature of between 300 and 800 ° C. and for a period of between 1 and 10 hours. 6 - Method according to one of claims 1 to 5 such that one implements between 2 and 10 successive treatments.